[entity] add a new `cw_linkable_rql` method
* the new method returns the entities that are or may be related to the
current one by the relation passed as an argument.
Closes #3738011.
option_group_changed('port', 'main', 'web')
option_group_changed('query-log-file', 'main', 'web')
option_group_changed('profile', 'main', 'web')
option_group_changed('max-post-length', 'main', 'web')